1. Field of the Invention
The present invention relates to an organic electroluminescent device comprising isolation regions, a method for producing same, a method of patterning a photosensitive resin composition and a photolithographic system. Precisely, the invention relates to a thin-film type, organic electroluminescent device in which the luminescent layer comprises an organic compound and which emits light when an electric field is applied to its luminescent layer, and also relates to a method for fabricating the device in which the microfabrication step is specifically improved. In addition, the invention relates to a method of patterning a photosensitive resin composition, in which the photosensitive resin composition has a reduced transmission of light at the wavelength of photoinitiation.
2. Discussion of the Background
Heretofore, it has been common that thin-film type electroluminescent (EL) devices arc made of inorganic materials which are obtained by doping a semiconductor of a Group III-V compound such as ZnS, CaS or SrS with Mn or a rare earth element (such as Eu, Ce, Tb, Sm) that serves as a radiative recombination center. However, the EL devices made of such inorganic materials have the following problems:
1) Alternate current drive is required (50 to 1000 Hz), PA1 2) The driving voltage is high (generally about 200 V), PA1 3) It is difficult to obtain full coloring (particularly, blue color), and PA1 4) Costs of peripheral driving circuits are high. PA1 wherein said deposition-preventing layer is formed by irradiation of a photosensitive resin composition wherein said photosensitive resin composition has a reduced transmission of light of wavelength .lambda. comprising a polymerizable compound; and a photoinitiator having an initiation wavelength .lambda..
However, in order to overcome the above problems, there have been activities, in recent years, to develop EL devices comprising thin organic films. Particularly, the light emission efficiency has been improved to a large extent over conventional EL devices employing a single crystal of e.g. anthracene, by the development of an organic EL device wherein the electrode material has been optimized for the purpose of improving the efficiency for carrier injection from the electrode in order to increase the light emission efficiency, and an organic hole transport layer made of an aromatic diamine and an organic luminescent layer made of an aluminum complex of 8-hydroxyquinoline, are provided (Appl. Phys. Lett., Vol. 51, p. 913, 1987). The light emission efficiency of the developed organic EL device is being on the practicable level.
Some methods have been tried for patterning the organic EL device.
One method comprises forming an anode film (or a cathode film) on a substrate, followed by forming thereon an organic luminescent layer (in this step, an organic hole transport layer and others are optionally formed). In this, a cathode film (or an anode film) is superposed on the organic luminescent layer through vacuum vapor deposition or the like using a shadow mask. In the organic EL device thus fabricated, a selected area between the anode and the cathode emits light but the other non-selected area does not. Therefore, the organic EL device can be so designed that the desired area therein can emit light.
Another method of using a resist has been tried, which comprises forming a luminescent layer through oblique incident deposition around a patterned resist wall (deposition-preventing layer) previously formed prior to the luminescent layer deposition (Japanese Patent Laid-Open No. 275172/1993). Still another method of using a resist has been tried, which comprises forming an additional overhanging layer to cover the resist pattern, or specifically processing the resist pattern to make it have a reverse-tapered cross-section profile, prior to forming the luminescent layer (Japanese Patent Laid-Open No. 315981/1996).
U.S. Pat. No. 5,294,869 discloses an organic EL device comprising a wall structure.
JP 8-315981 discloses an organic EL device in which an overhanging shape of a wall structure is formed from a plurality of layers.
JP 3-250583 discloses the formation of a wall structure.
Of the conventional patterning methods for fabricating organic EL devices, the method of using a shadow mask is problematic in that it requires accurate positioning of the substrate and the mask to the level of .mu.m in the chamber of the vacuum device, and the positioning operation is not easy. Another problem with the method is that the substance adhered to the mask forms a thick film thereon in the course of repeated deposition whereby the pattern of the mask becomes dull.
Of the conventional methods, the patterning method of oblique incident deposition is favorable to fabricating small-sized devices, but for large-sized devices, the method requires a large space for the substrate. In addition, in the method, the thickness of the film formed will differ between the source side and the opposite side on the substrate, and fine patterning is impossible in the method. The problem with this other conventional patterning method where the resist is covered with an additional overhanging layer or is specifically processed to have a reverse-tapered cross-section profile, is that the method requires complicated steps for forming the overhanging layer or for specifically processing the resist. In addition, the reproducibility of the intended taper profile in the method is low, and the method is therefore expensive.
Ochai et al. U.S. Pat. No. 5,916,713 discloses a photopolymerizable composition for a color filter comprising a (meth)acrylate, a photopolymerization initiator and a colorant.
Urano et al. U.S. Pat. No. 5,800,952 discloses a photopolymerizable composition for a color filter comprising a compound having at least one ethylenically unsaturated double bond, a photopolymerization initiator system, a colorant and a phosphoric (meth)acrylate compound and/or an organic carboxylic anhydride.
Urano et al. U.S. Pat. No. 5,863,678 discloses a photopolymerizable composition for a color filter comprising a compound having at least one ethylenically unsaturated double bond, a photopolymerization initiator system and a red, green or blue colorant.
Takasaki et al. U.S. Pat. No. 5,914,206 discloses a color filter having a resin black matrix on a transparent substrate.
Accordingly, the first object of the invention is to address problems with the conventional methods noted above and to provide an organic EL device with the radiative recombination probability in the non-selected area of the organic luminescent layer in the device being greatly reduced, for which a deposition-preventing layer having a predetermined profile is formed with accuracy to facilitate and ensure micro-patterning in fabricating the device.
On the other hand, the deposition-preventing layer in the conventional organic EL devices is to electrically isolate the element cells from each other, and is therefore made of an electric insulator. Accordingly, on the substrates of the devices, an insulator serving as the deposition-preventing layer is disposed in stripes or lattices. As a result, in the pre-treatment step to be effected after the deposition-preventing layer has been formed and before a luminescent layer is formed, or in the step of forming a metallic electrode film layer, the electrically insulating area of the deposition-preventing layer is charged up thereby interfering with the pre-treatment operation or the electrode film deposition. For example, the deposition-preventing layer of an insulator formed on the surface of a substrate is charged up during ordinary pre-treatment of plasma processing with a mixed gas of argon and oxygen, thereby often causing abnormal plasma discharging, with the result that the layer is partly broken to increase the probability of failed devices. On the other hand, where a metallic electrode film is formed through sputtering with high productivity after the formation of the deposition-preventing layer, the deposition-preventing layer is also charged up, thereby having some negative influences on the sputtering operation, with the result that the abnormally sputtered film will be uneven also to increase the probability of failed devices.
Accordingly, the second object of the invention is to address problems with the conventional EL devices in which the deposition-preventing layer formed is readily charged up in the course of the subsequent steps of forming the other element layers thereon, and to provide a high-performance organic EL device with few defects, for which the deposition-preventing layer formed in the device is so controlled that it is not charged up so as not to cause abnormal discharging or abnormal sputtering in the subsequent steps of forming the other element layers thereon, thereby increasing the good yield of high-quality devices with few defects.